The present invention relates to a method for fabricating a semiconductor device; and, more particularly, to a method for fabricating fine photoresist pattern to form a fine line width of about 0.1 xcexcm or less.
Generally, with the development of highly integrated circuits, the minimum feature size required to manufacture a semiconductor device has become increasingly smaller and line width has depended on the resolution of step-and-repeat projection equipment (stepper). The resolution of the current stepper may form a line width of 0.28 xcexcm when the i-line of 365 nm-wavelength is applied to the lithography process. In case of DUV (Deep Ultra Violet) of 275 nm-wavelength, the stepper may form a line width of 0.18 xcexcm.
The stepper has employed a DUV light source from KrF-Excimer laser generating 248 nm-wavelength light or a scanning method has been employed.
As of now, although many techniques are combined in order to increase of the resolution in the DUV-Lithography process, it is impossible to form a fine pattern of 0.1 xcexcm or less. Accordingly, new light sources such as electron beam, X-ray and EUV (Extreme Ultra Violet), have been developed.
However, the lithography process using the electron beam is not suitable to increase the throughput of semiconductor devices and, in case of the X-ray, there are many problems to be solved in connection with masks, arrangement, resist materials and the yield of devices.
On the other hand, photoresist patterns have been removed by plasma that is generated from the RF or microwave equipment. That is, the photoresist layers are removed by the chemical reaction on ions or radicals in the plasma, which physically strike against the components in the photoresist patterns.
However, this photoresist removing method involves a physical method, in which the ion and radical collisions are employed, and an additional chemical method. As a result, this methodology may cause an exposed semiconductor substrate or other layers formed on the semiconductor substrate to be damaged because many layers are exposed between the photoresist patterns. Also, heavy metal ions such as Na+ infiltrate into the semiconductor layer together with plasma components, causing the semiconductor layer to be seriously damaged. Frequently, this seriously damaged semiconductor layer results in the devices being discarded.
FIGS. 1A and 1B are cross-sectional views illustrating a prior art method for forming photoresist patterns.
Referring to FIG. 1A, a conducting layer 12 is formed on a semiconductor substrate 11 and an ARC (Anti-Reflective Coating) layer 13 is formed on the conducting layer 12. Photoresist patterns 14 are formed on the ARC layer 13 using a KrF-Excimer laser stepper. The photoresist patterns 14 are formed at a constant distance (S) and height (H) and in a constant width (W). Typically, the photoresist patterns 14 may have a width of 170nm in the KrF-Excimer laser stepper.
Referring to FIG. 1B, final fine patterns are formed by developing the photoresist patterns 14 to which the exposure process has been applied. However, in case where the ratio for the height to the width of each photoresist pattern 14 is in excess of four, the photoresist patterns 14 may collapse after wet-treating the photoresist patterns 14 in the developing process. Furthermore, the depth of the photoresist patterns 14 may be decreased at the time of treatment in a plasma asher with their size shift.
The disclosed method and device provides a method for forming fine patterns capable of surpassing resolution of a stepper by using a KrF-Excimer laser and an O3-asher in semiconductor fabricating processes.
The disclosed method and device also provides a method for forming fine patterns to guarantee the throughput of devices in semiconductor fabricating processes.
In accordance with one aspect of the present invention, a method for forming fine photoresist patterns in a semiconductor device is provided which comprises forming photoresist patterns over a semiconductor substrate using a stepper; and ashing the photoresist patterns using oxygen radicals in order to decrease line width of the photoresist patterns. In the disclosed method and device, the oxygen radicals are formed by a thermal decomposition of an ozone gas in an ozone asher.